Enhancement of tick‐borne encephalitis virus transmission by tick salivary gland extracts

Abstract

To investigate the role of ticks in TBE virus transmission, salivary gland extract (SGE) was derived from partially fed female Ixodes ricinus, Dermacentor reticulatus and Rhipicephalus appendiculatus ticks. Guinea-pigs were infested with uninfected R. appendiculatus nymphs and inoculated with a mixture of TBE virus and SGE or with virus alone. The number of ticks which on average acquired virus from feeding on animals inoculated with TBE virus and SGE from partially fed ticks was 4-fold greater than the number that became infected by feeding on animals inoculated with virus alone or virus plus SGE from unfed I. ricinus. Viraemia was detected in 67% of guinea-pigs inoculated with virus plus SGE compared to 30% of guinea-pigs inoculated with virus alone. Virus titres in the blood were similar for both groups of animals [range 2.0-2.8 log10 plaque-forming units (PFU)/ml of blood]; however, the number of ticks that became infected was significantly higher on animals inoculated with virus plus SGE from partially fed ticks. No significant difference was observed with respect to the tick species used to derive SGE. The results indicate that TBE virus transmission is enhanced by factor(s) associated with the salivary glands of feeding ticks, and that these factor(s) may facilitate efficient transmission of TBE virus between infected and uninfected ticks even when they feed on hosts that have no detectable viraemia.

Persistence and transmission of tick-borne viruses:Ixodes ricinusand louping-ill virus in red grouse populations

“…Non-viraemic transmission has been demonstrated for both Thogoto virus (Orthomyxoviridae) and the flavivirus that causes tick-borne encephalitis (TBE) throughout Europe and Eurasia. Such a process only occurs when ticks are feeding close to one another and is probably enhanced by the presence of tick saliva (Labuda et al 1993). In epidemiological terms, the largest effects of non-viraemic transmission will be to provide a background force of tick infection, the scale of which depends on the proportion of infectious ticks and particularly infectious larvae the non-viraemic host produces.…”

Sandfly Maxadilan Exacerbates Infection with Leishmania major and Vaccinating Against It Protects Against L. major Infection

“…While enhanced blood flow insures the feeding success of the arthropod, inhibiting the immune response of the host may prevent the host from becoming sensitized to the bite of the arthropod. However, there is now mounting evidence that the saliva of an arthropod vector can also enhance the infectivity of pathogens that the arthropod transmits (5)(6)(7)(8)(9)(10). Therefore, injecting arthropod-borne pathogens by syringe does not mimic natural transmission.…”

Effect of salivary gland extract from Ixodes ricinus ticks on the proliferation of Borrelia burgdorferi sensu stricto in vivo

“…Tick saliva-activated transmission of various tickborne pathogens has been demonstrated (Jones et al 1989, Labuda et al 1993, Kročová et al 2003. In the case of Borrelia spirochetes, Pechová et al (2002) reported indirect evidence for increased bacteraemia in mice injected with B. afzelii plus Ixodes ricinus SGE compared with SGE-untreated control mice.…”

“…After 5 days, engorged ticks were removed and the salivary glands were dissected and pooled. The 5-day period, for which the ticks had fed on guinea pigs, was chosen due to the best effect of SGE prepared from such ticks on the saliva-activated transmission of TBE virus (Labuda et al 1993). After washing in phosphate-buffered saline (PBS), the salivary glands were homogenized in 1 ml PBS by sonication and centrifuged at 10,000 g for 10 min.…”